<!DOCTYPE html>
<html lang="en">
<head>
    <meta charset="UTF-8">
    <meta http-equiv="X-UA-Compatible" content="IE=edge">
    <meta name="viewport" content="width=device-width, initial-scale=1.0">
    <title>Document</title>
    <style>
        #father #son {
            color: blue;
        }

        #father p.c2 {
            color: red;
        }

        #father {
            color: green !important;
        }

        div#father .c1 {
            color: yellow;
        }
    </style>
</head>
<body>
    <div id="father" class="c1">
        <p id="son" class="c2">
            这行文本时什么颜色的？
        </p>
    </div>
</body>
</html>